JavaBeans PropertyChangeSupport Trick

I’ve always written bound properties like this:

public class Rect {
  private PropertyChangeSupport changes = new PropertyChangeSupport(this);
  private int width;

  public void setWidth(int width) {
    int old = this.width;
    this.width = width;
    changes.firePropertyChange("width", old, width);
  }
}

I just realized that the 3-line setWidth(...) method can be compressed to a single line:

public void setWidth(int width) {
  changes.firePropertyChange("width", this.width, this.width = width);
}

It seems like this might reduce a significant amount of boilerplate code for some types of apps.

UPDATE

As pointed out in the comments, for non-primitive properties, null values (both old and new) will trigger unwanted events. Although generally harmless, firing too many events can cause significant performance problems, particularly if you trigger repainting in the GUI for properties that didn’t really change.

So you might want to do this:

public void setName(String name) {
  if (this.name != null || name != null) {
    changes.firePropertyChange("name", this.name, this.name = name);
  }
}

Or this, depending on your style:

public void setName(String name) {
  if (this.name == null && name == null) {
    return;
  }
  changes.firePropertyChange("name", this.name, this.name = name);
}

Posted on Saturday, December 15th, 2007 at 5:20 pm in Java.